The invention relates to motor controllers. More specifically, the invention relates to a compact motor controller design which has improved drawout capabilities.
Motor controllers are used to control electrical equipment such as motors and transformers. Typically, a motor controller provides some form of short circuit protection such as a circuit breaker or a fuse, a way to connect and disconnect power to the load such as a vacuum contactor or an air-break, and overload protection such as an overload relay. The motor controller also provides some way to disconnect the motor controller from the main power supply for maintenance on the motor controller. This typical arrangement may be varied to suit a particular application.
Conventional motor controllers and motor controller features are illustrated and described in U.S. Pat. No. 4,739,672, entitled "Mechanical Interlock for a Vacuum Contactor" and issued to John D. Kleinecke et al. on Apr. 26, 1988; U.S. Pat. No. 4,448,450, entitled "Defeatable Handle and Interlock for Electrical Equipment Enclosure" and issued to John D. Kleinecke et al. on May 15, 1984; U.S. Pat. No. 4,427,854, entitled "Racking Mechanism for Motor Control Center" and issued to John D. Kleinecke et al. on Jan. 24, 1984; U.S. Pat. No. 4,463,408, entitled "Two-High Motor Control Center with Staggered Cubicles" and issued to John D. Kleinecke et al. on Jul. 31, 1984; U.S. Pat. No. 4,482,892, entitled "Caution Lamp for High Voltage Controller" and issued to Samir F. Farag et al. on Nov. 13, 1984; U.S. Pat. No. 4,652,966, entitled "Solenoid-Actuated Mechanical Interlock for a Motor Controller" and issued to Samir F. Farag et al. on Mar. 24, 1987; U.S. Pat. No. 4,454,564, entitled "Fabricated Carriage Assembly for High Voltage Contactor" and issued to Thomas R. Little et al. on Jun. 12, 1984; and U.S. Pat. No. 4,447,858, entitled "Rigid Subchassis Structure for Motor Control Center or the Like" and issued to Samir F. Farag et al. on May 8, 1984. The entire contents of these patents are incorporated herein by reference.
Conventional motor controllers may include a drawout unit which can be withdrawn from the motor controller housing to access certain components. Access to the vacuum contactor, power fuses, and other equipment is required during initial installation and for periodic maintenance. In some conventional designs withdrawal of the drawout unit is used for power isolation. Such conventional drawout units are provided with a set of wheels which roll on a track in the motor controller compartment. The wheels and associated track facilitate movement of the drawout unit and also serve to guide the drawout unit into proper alignment with the fixed portion of the motor controller. The electrical power source is isolated by disconnecting spring-loaded finger assemblies called "stabs." The stabs rely on springs to maintain contact pressure between fixed and moveable parts.
Motor controllers are commonly stacked in a single enclosure, for example, "two-high." In a two-high arrangement the motor controller compartment height for each controller must be 45 inches or less, in order to maintain the standard maximum overall enclosure height of 90 inches.
FIG. 1 illustrates the arrangement of a conventional motor controller design. FIG. 1 illustrates a front view of a medium voltage (MV) motor controller 100. Due to height restrictions, in this conventional design current transformers 110 and outgoing cables 120 are located to the left side of the other major components. (In FIG. 1, the second and third sets of current transformers and outgoing cables are obscured by the first set.) Internal cables 130 connect the current transformers 110 to load terminals 140 of the vacuum contactor.
In this conventional arrangement, the narrowest motor controller enclosure width obtainable is 36 inches due to the size of the major components and their traditional arrangement.